Track 1 • Module G4 of 4 • How the Global Internet Routes Packets

BGP (Border Gateway Protocol) & Autonomous Systems

How does a packet leave your office in New York and find the fastest fiber-optic path across 5 different telecom providers to reach a server in Tokyo—and automatically reroute if a cable is cut? Meet BGP (Border Gateway Protocol), the routing glue of the global Internet!

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The Airline Hub & Passport Stamp Analogy: The Internet is made of thousands of independent networks called Autonomous Systems (AS) (each with a number like AS 701 or AS 13335). When AS 13335 announces "I own IP block 93.184.216.0/24", every network that passes the announcement along stamps its own AS number onto the AS_PATH list. By default, your BGP router simply counts the stamps and picks the path with the fewest Autonomous System hops!
☁️ Continue to Track 2: AWS Cloud Networking → ← Prev: Module G3 (NAT & Firewalls)
Interactive Multi-AS BGP Routing, Fiber-Cut Failover & RPKI Simulator
🏢 Your Network ASN: AS 65001 🧭 Edge BGP Router Dual-Homed to 2 ISPs BGP Best-Path Order: 1. Highest LOCAL_PREF 2. Shortest AS_PATH 3. RPKI Origin Check: ON 📡 Primary ISP A (AS 701) Announces: 93.184.216.0/24 AS_PATH: [701, 13335] (2 Hops!) LOCAL_PREF: 100 (Default) ✓ Fiber Link UP (Direct to AS 13335) 🌐 Backup ISP B (AS 3356) AS_PATH: [3356, 174, 13335] (3 AS Hops via AS 174) LOCAL_PREF: 100 🔀 Transit C (AS 174) Intermediate Carrier Path: [174, 13335] 🕵️ Rogue Network (AS 666) Falsely Announces: 93.184.216.0/24! Fake AS_PATH: [666] (1 Hop!) 🛡️ RPKI Status: INVALID (Blocked by ROA!) Attempts BGP Prefix Hijack 🎯 Destination Network ASN: AS 13335 🌐 Target Server 93.184.216.34:443 Originates Prefix: 93.184.216.0/24 Signed RPKI ROA: Origin = AS 13335 Only
Shortest AS_PATH = Default BGP Winner LOCAL_PREF = Overrides AS_PATH for Outbound Traffic Engineering RPKI = Cryptographically blocks BGP Prefix Hijacks
← Step G3: NAT, PAT & Firewalls ☁️ Graduate to Track 2: AWS Cloud Networking Course →